1. Field of the Invention
The present invention relates to a dual-mode dividing wall column that is capable of mode switching between a dividing wall column operating mode and a conventional column operating mode, and a method of distilling a crude feed material including ethylene or propylene using the dual-mode dividing wall column.
2. Description of the Related Art
Since various feed materials such as crude oil are generally mixtures of many chemicals, it is unusual to use feed materials themselves for industry, and it is usual to use feed materials after separating the feed materials into each chemical. A representative process among chemical processes of separating a mixture is a distillation process.
In general, in the distillation process, the mixture is divided into two, i.e., a high boiling point component and a low boiling point component. Thus, (n−1) columns that are one less than the number (n) of components of the mixture to be separated are used. That is, a two consecutive column structure is mainly used in a process of separating a three-component mixture according to the related art in a distillation industrial site.
The distillation process for separation of a three-component mixture according to the related art is shown in FIG. 1. For example, a two column method, whereby a first column 11 separates a lowest boiling point component D from the mixture and a second column 21 separates a medium boiling point component S and a high boiling point component B from the mixture. In this case, remixing of the medium boiling point component S generally occurs in a lower region of the first column 11. In detail, in the distillation process according to the related art, composition of a product can be easily controlled, while a remixing procedure of the medium boiling point component S occurs in the first column 11, which is a main cause of lowering thermodynamic efficiency of the column and causes additional and unnecessary consumption of energy.
There are many researches on a new distillation structure so as to solve the problems. A representative example of improving separation efficiency using a thermally integrated structure may be a Petlyuk column structure as shown in FIG. 2. In the Petlyuk column, a pre-fractionator 12 and a main column 22 are arranged in a thermally integrated structure so that a low boiling point component and a high boiling point component are primarily separated from a mixture using the pre-fractionator 12, and then a column top part and a column bottom part of the pre-fractionator 12 are introduced into a supply stage of the main column 22 and the main column 22 separates a low boiling point component, a medium boiling point component, and a high boiling point component, respectively, from the mixture. In such a structure, a distillation curve in the Petlyuk column is similar to an equilibrium distillation curve, and energy efficiency is improved. However, design and operation of a process are not easily performed, and in particular, it is difficult to keep a pressure balance in the Petlyuk column. In order to overcome limitations of the Petlyuk column, a dividing wall column (DWC) has been proposed. In detail, the DWC is similar to the Petlyuk column in terms of thermodynamics; however, in terms of a structure, the DWC has a shape in which a dividing wall is installed in the column so that the pre-fractionator of the Petlyuk column is integrated into the main column. This structure is conducive to naturally removing a difficulty of a pressure balance between the pre-fractionator and the main column of the Petlyuk column and a difficulty of an operation caused by the difficulty of the pressure balance so that the operation of the column can be easily performed, two columns are integrated into one, and investigation costs can be remarkably reduced.
For example, as prior arts for the DWC, Korean Patent Laid-open Publication No. 2010-0105500 discloses a dividing wall column for producing 2-ethylhexaneol, and Korean Patent Laid-open Publication No. 2010-0092396 discloses a dividing wall column including a pressure equalization unit.